The invention relates to the field of aircraft ground proximity warning systems and, in particular, to systems that warn of a negative rate of climb after takeoff or during a missed approach.
In the prior art systems, as specifically represented by the U.S. Pat. application of Bateman, Ser. No. 480,727, filed on June 19, 1974, entitled "Aircraft Ground Proximity Warning Instrument," assigned to the assignee of this application, a warning signal is sounded during the takeoff or missed approach phase of aircraft operation whenever there is an indication of a negative rate of climb, i.e. a momentary descent toward the ground. In the prior art system, the takeoff or missed approach phase of operation is indicated to the warning instrument by means of signals representing the flight configuration of the aircraft, such as flap and landing gear settings. In addition, this particular warning mode is operative only at altitudes of from 50 feet to 700 feet above ground where it is assumed that in normal operation the aircraft will be climbing. However, there are circumstances under which during a normal takeoff and climbout the aircraft will level off below this 700 feet level. In the prior art systems even a momentary negative climb rate of 100 feet per minute triggers the warning signal. In addition to takeoff, a missed approach procedure, where this particular warning mode is also operative, would also tend to generate warnings if the pilot does not follow the missed approach procedure precisely as directed. Both of these circumstances will give rise to unnecessary or nuisance warnings which may reduce the confidence that air crews place in the warning system.
One approach to eliminating this problem would involve increasing the required negative climb rate to a value greater than 100 feet per minute, for example 500 feet per minute, but this would have the undesired effect of eliminating valid warnings where the aircraft continues to descent toward the ground at a relatively low descent rate.